Omnidirectional Aerosol Sampling Intake

ABSTRACT

An aerosol sampling intake configured to exclude particles generally greater than 20 microns AD and capture particles of less than about 10 microns AD with high efficiency, independent of weather conditions, through which air is sampled by suction. The intake combines an omnidirectional horizontal segment with diffuser and elbow, the elbow transitioning flow to a vertical segment, the vertical segment with overhanging lip, the centrifugal impactor for self-cleaning operation, thus relieving the dual problems of re-entrainment of particles bouncing from the impactor surface and fouling by particles sticking to the impactor surface. The device is adapted for use on moving vehicles, for sampling at increased windspeeds, or for sampling in rain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)from U.S. Provisional Patent Application No. 61/317,192 filed Mar. 24,2010; said patent document being incorporated herein in entirety for allpurposes by reference.

GOVERNMENT SUPPORT

This invention was made with government support under GrantN00178-07-C-3034 awarded by DOD. The US Government may have certainrights in the invention.

FIELD OF THE INVENTION

The present invention relates to a weather-resistant omnidirectionalintake for aerosol sampling and to devices and methods for classifyingaerosols into informationally-rich and informationally-poor particletypes.

BACKGROUND

Devices and methods for sampling and analysis of airborne particles(aerosols) from a moving airstream find use in environmental andindustrial sciences and for surveillance. The most informative aerosolparticles for the purposes contemplated here are those less than 20microns in apparent aerodynamic diameter (AD), and particularly thoseparticles of about or less than 10 microns AD, because these particlesremain suspended in air for longer periods of time and more readilypenetrate and lodge in the respiratory tract.

Aerosol sampling is made more difficult by wind, mist, dust and rain,and can be complicated when the aerosol sampling device is mounted on amobile vehicle such as a truck, airplane, marine vessel or riverinevehicle. Design of a sampling inlet can also be problematic because ofthe accumulation of sand, salt crystals, dust, and fibers, and alsowater spray. Under heavy loading, particulate solids such as dust andfibers have been known to accrete so as to block the sampling inlet orreduce sampling efficiency and performance. Filter pads sometimes usedfor trapping aerosols also become blocked or tear when wetted by rain ormist.

Improvements are needed in the art to develop a sampling inlet that isresistant to weather and effectively samples the mostinformationally-rich particles from moving airstreams, i.e., those lessthan 20 microns AD. Because the direction of flow of the movingairstream can shift, an omnidirectional sampling inlet is needed. Such adevice must be effective when mounted in a moving vehicle or stationarywhile subjected to increased surface winds, for example.

Ideally, the sampling inlet has a high efficiency in collectingparticles less than 10 microns AD and a high efficiency in excludingparticles greater than 20 microns AD under a range of ambientconditions, while not affected by changes in apparent windspeed or byrain. Advantageously, the device is also resistant to fouling by dust orfibers and is self-cleaning.

Wedding, in U.S. Pat. No. 4,461,183, describes an omni-directionalaerosol sampler with cylindrical external housing (1), internal skirtedflow deflector (2), and cyclonic particle fractionators, ie. havingairfoil-shaped vanes for forming a cyclonic flow in the downtube. Asshown in FIG. 1, a flow of air through the device is pulled by adownstream vacuum and is made cyclonic by airfoil-shaped vanes (3) atthe inlet (4) to the particle fractionator. The particle fractionatorconsists of a vertical, blind-bottomed, tubular trap (5) for receivingthe downwardly directed vortex through a narrow downtube (6) mountedcentrally under the vanes (3) and extending into the trap (5), such thatair entering the trap must reverse course and rise to exit through anannular outlet (7) at the top of the fractionator. The device isconfigured so that half the particles greater than 10 microns impact thewalls of the particle fractionator and are collected in the trap (5).The aerosol is thus classified into a coarse fraction, which is trappedin the device, and a fine fraction that exits the device and may becaptured on a filter cassette. The airfoil-shaped vanes are described asa two-dimensional shape (Col 4, lines 42-47) that is effective ineliminating particle deposition or build up. A lower flared portion ofthe skirt (8) directs air upwardly into the vanes (3). The curvature anddiameters of the intake duct (9) are selected so as to preventturbulence or deposition of particles upstream from the vane assemblyand trap (Col 5, lines 1-3). Thus particle removal occurs in and on thewalls of the trap (5), which functions as a cyclonic impactor. Thisdesign is inherently not self-cleaning and cannot continue to functionwithout period emptying of the trap. Condensate collecting in the trapcannot be drained without disassembly. It is thought that continuedbuildup of particles in the intake duct (9) will interfere withoperation of the device. Relatively little consideration is given to theflow conditions around the bottom of the skirt so as to avoid externalpressure ridges that would act to deflect and exclude sampling ofsmaller particles.

Cyclonic impactors are associated with increased inelastic impactorcollisions unless used in conjunction with wetted wall devices and thustend to take in an excess of larger particles that escape impaction bybouncing off the impactor surface.

The device also includes an internal bug screen. The device of FIG. 1Bis reportedly scaled to draw 113 to 1133 liters/min (4 to 40 cfm) and tooperate in windspeeds up to 24 kilometers per hour (15 miles/hr). Athigher windspeeds, collection of particles in the desired size range maybe impeded because of impaction in the intake manifold, whichunfortunately functions as an inertial or bluff body impactor. Also, thetrap is not readily cleaned and may clog or fill with condensate, fibersand dust during operation under adverse conditions.

Interestingly, the preferred system currently in use is not the Weddingdevice but rather the device (20) of FIG. 2, which is adapted fromcompressor intakes with noise-suppression, and is used by the USDepartment of Defense in their Dry Filter Unit 2000 particle capturetechnology. This unit is used in conjunction with a standardized duplexfilter cassette which is removed periodically for immunoanalysis.Particles entering the updraft tubes (21) are classified by elutriation,and the particle depleted fraction is then directed to the vacuumexhaust. Elutriation is known to have a relatively poor particle sizeresolution capability and a broad cutsize limit. We have found that theunits have relatively low efficiency in capture of informationally-richparticles with increasing wind speed. The unit is not self-cleaning andparticles frequently accumulate in the housing (22) between the updrafttubes (21). Also, moisture that enters the filter cassette can lead tofalse negatives. The system would benefit from increased sensitivity,improved cutsize resolution, and better wind-resistance.

One improved system is shown in FIG. 3. This system uses an eductor (31)with inertial impactor (32) to separate coarse material from a bendingflow stream that is then directed onto a duplex filter cassette (33).The duplex filter cassette is the same as the one used with the DryFilter Unit 2000 developed by the Department of Defense. The inlet units(30) are designed to be stacked for storage and feature a hinged housingfor easy access to the filter cassette. Unfortunately, this prior artdevice is relatively inefficient at classifying particles by size due toits geometry and the close proximity of the inertial impactor andsampling cassette, which may allow entry of raindrops and is associatedwith accumulation of condensation inside the ductwork due to lack ofdrainage. Also at issue is the higher pressure drop, power loss andpotential for fouling because inlet flow is passed through a smallconstriction.

As is also known in the art, downstream virtual impactors, cascadingvirtual impactors, bluff-body impactors, liquid impingers, filters, andthe like may be used to further concentrate, classify or capture aerosolspecies by size or composition. While these techniques are well known,the design of the initial sampling inlet remains problematic because ofinstabilities of the outside air mass relative to the intake and becauseof lack of streamlining of the outside housing of the intake. Also ofconcern, the inlet may not be self-purging of coarse particles andfibers, or of water vapor or rain.

In U.S. Pat. No. 6,530,287 to Rodgers, a rain shroud covers cantedintake nozzles spaced around a central chamber; the intake nozzles arecanted so as to drain moisture that enters under the shroud whileadmitting particles. This unit lacks capacity to fractionate particlesby size and is generally non-specific in admitting large and smallparticles into the central chamber.

Accordingly there remains a need in the art for improved devices andmethods for omnidirectional collection of aerosols that overcome theabove disadvantages.

SUMMARY

Generically, the invention is an omnidirectional sampling intake forcollecting informationally-rich particles from a moving air column andrejecting informationally-poor particles. The invention overcomescertain difficulties of the prior art in that it is a) effective inclassifying and sorting informationally-rich and informationally-poorparticles and is effective over a range of wind speeds and weatherconditions, and b) is provided with self-cleaning features. Theinventive intake takes advantage of a combination of centrifugal andgravitational forces on particles to achieve these effects and is thusan “elutriatively-assisted centrifugal impactor”. Combined are ahorizontal omnidirectional flow path, a first centrifugal impactorsection or elbow that transitions aerodynamically to a vertical flowpath, and an overhanging lip at the top, which forms a centrifugalimpactor that is self-cleaning in operation. The horizontal segment isoptionally a diffuser. Unlike devices of the prior art, the inventionovercomes a notorious difficulty in excluding particles that “bounce”off an inertial impactor surface from re-entering the intake streamlinesand undesirably being re-entrained in the airflow through the device.

Most larger particles are excluded by centrifugal inelastic impaction inthe elbow from horizontal to vertical flow. Particles that experienceelastic collisions on the impactor surface will reflect from the surfacebut most likely will remain in the flow boundary layer where airvelocity is low. These re-entrained particles are further classified byelutriation in the vertical flow path segment of the inventive intakemanifold. This combination of the precision of centrifugal impactorgeometry with the re-entrainment resistance of an elutriative classifierhas not previously been reported and is surprisingly effective inrejecting oversize, informationally-poor material. As a result, we areable to report our results on a linear particle diameter axis ratherthan a log particle diameter axis (compare FIGS. 9 and 10 herein versusFIG. 18 of US Patent Application 2009/0223279, for example) and achievea D₀ of 20 microns over a range of windspeeds.

In the inventive device, larger particles that impact in the intakemanifold either drop down and away from the intake or adhere to theimpactor surfaces until removed by a cleaning action. Smaller particles(i.e., those which are most relevant to the biological and chemicalmonitoring applications of the intake manifold of the invention) are notimpacted and are swept with the streamlines into a collector duct, wherethey may be quantitated, concentrated or collected for further analysis.Streamlines in the intake manifold are non-cyclonic, reducing losses ofinformationally-rich particles that are likely as the path length isextended.

Mist is an example of a relatively “information-poor particle”. Afteracceleration in the intake inlet, fine mists are effectively trapped bycentrifugal forces on the vertically disposed impactor surface, butwould not be trapped by elutriation alone. Mist coalesces to form waterdroplets that are shed from the vertical impactor surfaces, thuscleaning the impactor of salts and solids. Airborne salt spray isanother information-poor particle. Information rich particles includeparticles containing microorganisms, including bacteria, fungi andviruses, particles containing toxins, noxious or irritating particles,and particles containing chemical reactants, for example. Informationrich particles are typically less than 20 microns in diameter, mostfrequently about or less than 10 microns in diameter, because theseparticles remain suspended in an air column and are likely to penetratethe respiratory system. The intake manifold is configured so that theseparticles of interest follow the air streamlines through the intake andmay be concentrated, collected or analyzed downstream by a variety oftechniques known in the art.

A variety of concentrative and analytical downstream devices may be usedwith the intake manifold of the present invention, including for examplethe aerodynamic lens and skimmer assemblies of U.S. Pat. Nos. 7,704,294and 7,875,095, which are co-assigned.

Interestingly, at higher windspeeds, windstreams passes through theopening of the inlet slot, the horizontal flow path segment, and thefirst elbow section. Smaller particles are diverted into the collectorduct under suction, but the wind acts to scour out rejected particlesthat were previously deposited within the intake manifold or captured onthe impactor intake duct surfaces, another self-cleaning feature of theinvention.

The inventive intake manifold is typically spar-mounted in use. Thedevice is mounted on a mast so as to reduce surface ground effects suchas intake of road dust when mounted on a moving vehicle. The shape ofthe housing bonnet is made aerodynamic to minimize formation of apressure ridge on the windward edge of the sampling intake, which coulddivert smaller particles from the intake, and leeward eddies that couldpropagate into the internal flow channel. The circumferential leadingedges of the intake are made knife sharp to cut streamlines that flowaround and into the sampling inlet, which is a narrow slit thatencircles the sampler. The bonnet is designed to shed rain andaerodynamically is configured for minimal drag and bow wave when exposedto wind. Happily, the more efficient internal design serendipitouslyresults in a more aerodynamic housing design.

In a first embodiment, the invention is an omnidirectional wind and rainresistant intake for collecting a particle concentrate ofinformationally-rich particles, where the particle concentrate isimpactingly and elutriatively depleted of informationally-poor particlefractions, including oversize material and rain droplets. The intakemember is a housing made up of a rain bonnet plate and a baseplate. Thetwo plates are spaced apart to form an internal manifold with flowpaththerebetween and are separated by an intake slot all around the twoplates. The internal manifold also has an outlet port generally on acenter axis, a first inside surface formed by the bonnet plate and asecond inside surface formed by the baseplate. The internal manifoldfunctions to direct a suction airflow from the intake slot to the outletport along a flowpath between the inside surfaces and to separateinformation-rich particles and information-poor particles, rejectingparticles that are oversized such as sand, road grit, raindrops and soforth. The internal manifold thus functions as an elutriatively-assistedimpactor and may include, in order of passageworks therethrough:

a) a horizontal flow section for ordering a suction airflow intohorizontal streamlines and for elutriatively removing a first cut of theinformation poor particles from the suction airflow according to a firstcut-off size;b) a first centrifugal impactor section fluidly joining the horizontalflow section to the outlet port, the first centrifugal impactor sectionfor impactingly removing a second cut of the information poor particlesfrom the suction airflow according to a second cut-off size; where thefirst centrifugal impactor section is generally an elbow turntransitioning the horizontal section to a vertical updraft section ofthe flowpath;d) a contoured overhanging lip forming an elutriative centrifugalimpactor, where the overhanging lip is positioned around the top of acentral pillar;e) a narrow rounded passage between the uppermost crown of the centralpillar and an apposing inside surface of the bonnet plate;f) optionally a flow guide for smoothly bending the direction of flowdownward, andg) a descending collector duct or downslip tube on the center axis thatmay be fluidly connected to a downstream suction pump or blower.

In one aspect of the invention, the inlet slot between the plate edgescomprises upper and lower inlet lips, the upper lip formed on the bonnetplate and the lower lip formed on the baseplate, the upper lip having anupper lip inside surface and a the lower lip having a lower lip insidesurface, and wherein the upper inside lip surface is generallyhorizontal to a ground plane and the lower inside lip surface is angledup along the flow path at a generally planar angle or flare of less than45 degrees, more preferably 5-30 degrees, thereby forming a convergingannular entrance to the flow path to compensate for any ground boundarylayer effect and any deflection of excluded windstreams around or overthe bonnet plate.

The horizontal flow section is optionally a diffuser section, having agenerally diverging inside upper surface and second lower surface withincreasing distance from the intake slot, the diffuser flow for slowingstreamline velocities and for sharpening the first cut-off size.

The elbow segment of the flowpath functions for bending and acceleratingthe horizontal streamlines as generally vertically-directed streamlines,transitioning the flow path to an elutriatively-assisted impactorsection. The elutriatively-assisted impactor section comprises upwardlyconverging inside surfaces, a first inside surface forming a generallybell-shaped female surface and a second inside surface forming agenerally pillar-shaped male surface with crown. The pillar-shaped malesurface matingly conforms to the female surface with space for theflowpath annularly converging between. The crown of the pillar issurrounded by a radiused annular lip or collar projecting into theflowpath, the projecting radiused annular lip with underside impactorsurface for impactingly capturing the information-poor particles withelutriative assist, thereby excluding the informationally poor particlesfrom the suction airflow and conveying the informationally richparticles over the radiused annular lip. We believe that anelutriatively-assisted centrifugal impactor with self cleaning featuresis an advance in the art.

Uses of the present invention include detection of biological orchemical warfare agents in the form of aerosols, collection ofindustrial pollutant particles such as fly ash in a gas plume, samplingof air in buildings associated with “sick building” syndrome, collectionof infectious or disease causing organisms in hospitals and publicspaces, the collection of radioactive particles, and collection ofbiological aerosols such as endotoxins, indoor and outdoor allergens,monitoring of industrial pollution, and so forth. It is alsocontemplated that the present invention may be used for the detectionand collection of airborne particles associated with illegal drugs andexplosives, or their precursors.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be more readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIGS. 1A-B are cross-sectional drawings of a prior art sampler intakedepicted in U.S. Pat. No. 4,461,183 to Wedding. FIG. 1C is a sectionalview of the head of the sampler.

FIG. 2 is a cutaway view of a prior art sampler used with the Dry FilterUnit 2000.

FIG. 3 is a cross-sectional view through a sampler intake developed bythe University of Minnesota for the Department of the Navy.

FIG. 4 depicts a first embodiment of an omnidirectional sampling intakeof the invention, shown here in elevation view.

FIG. 5 depicts an omnidirectional intake of the invention in perspectiveview; showing wind moving across the aerodynamic sampling head.

FIG. 6 shows an omnidirectional intake of the invention incross-section.

FIG. 7 is a perspective cutaway view of an omnidirectional intake ofFIG. 6.

FIG. 8 describes the internal airways of an omnidirectional intake ofthe invention.

FIG. 9 is a modeling performance for particle classification and captureefficiency, inset with a comparison to the standard inlet of FIG. 2.

FIG. 10 is a plot showing measured performance versus modeledperformance for particles of 3 and 7 microns AD at a windspeed of 10mph.

FIG. 11 describes a general rationale and methodology for use of anomnidirectional intake of the invention in an aerosol sampling protocol.

FIG. 12A is a second embodiment of an omnidirectional sampling intake ofthe invention.

FIG. 12B shows a detail of the vanes used in the omnidirectional intakeof FIG. 12A.

FIG. 13 describes a third embodiment of the invention with internalsupport rod for removable bonnet.

FIG. 14 describes a collar assembly for the baseplate, the collar havinga tubular ultrasonic transducer for assisted cleaning.

NOTATION AND NOMENCLATURE

Certain terms throughout the following description and claims are usedto refer to particular features, steps or components. As one skilled inthe art will appreciate, different persons may refer to the samefeature, step or component by different names. This document does notintend to distinguish between components, steps or features that differin name but not in function or action. The drawing figures are notnecessarily to scale. Certain features or components herein may be shownin somewhat schematic form and some details of conventional elements maynot be shown in the interest of clarity and conciseness.

Certain meanings are defined here as intended by the inventors, ie. theyare intrinsic meanings Other words and phrases used here take theirmeaning as consistent with usage as would be apparent to one skilled inthe relevant arts.

“Aerodynamic diameter” (AD) is the diameter of a virtual sphere of unitdensity (1 g/cm³) that attains the same terminal settling velocity(v_(s)) at a low Reynolds number as the actual physical particle underconsideration. For mathematical modeling purposes, it is convenient toexpress the behavior of an irregularly shaped particulate specimen as ifit were a spherical particle, making it easier to predict, compare andcorrelate various materials. Typically, the density of a particulatesample is not known during field sampling and calculations are generallyperformed assuming unit particle density (1.0 g/cm³).

“Cut-off size” (D₅₀)—is defined as a particle size, generally asaerodynamic diameter, for which 50% of the particles of that size areseparated from an airflow under specified conditions of operation.

D₀ refers to a cut-off size taken as essentially 100% exclusion, whichindicates that a particle exceeding a critical diameter D₀ is excludedfrom an airflow.

“Informationally-rich particle”—refers generally to a particle having anaerodynamic diameter of less than 20 microns, and particularly to aparticle having an aerodynamic diameter of less than or about 10microns. In contrast, informationally-poor particles are generally thosegreater than 20 microns in diameter, and include dust, mist, fog, andraindrops, which have little or no significance in the applicationsdescribed here. Informationally-poor particles are generally “oversized”particles, exceeding a cut-off size for rejection by the intake.

“Anisokinetic” sampling is a condition in which the mean velocity of theambient airstream differs from the mean velocity of the air entering theintake manifold.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, particular features, structures, orcharacteristics of the invention may be combined in any suitable mannerin one or more embodiments.

“Conventional”—refers to a term or method designating that which isknown and commonly understood in the technology to which this inventionrelates.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense: that is, as “including, but not limited to”.

DETAILED DESCRIPTION

Although the following detailed description contains many specificdetails for the purposes of illustration, one of skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the invention. Accordingly, the exemplaryembodiments of the invention described below are set forth without anyloss of generality to, and without imposing limitations upon, theclaimed invention.

Intake (or “inlet”) efficiency is a function of aspiration efficiencyand transmission efficiency. Overall efficiency is also determined bythe downstream capture or collection efficiency, which is generally veryhigh, but is determined by a capture device such as filter membrane orliquid impinger which is generally downstream from the intake manifoldper se.

η_(overall)=η_(aspiration)+η_(transmission)+η_(capture)

Since downstream capture efficiency, such as by filtration, is generallyvery high, the upstream cutoff and exclusion limits of the intakemanifold to a great extent determine whether performance of overallairborne particle capture and analysis is satisfactory for theapplication. Thus significant attention to efficient admission ofinformationally-rich particles and efficient exclusion ofinformationally-poor particles are both relevant to intake manifoldperformance.

In the design of the present invention, a novel combination ofelutriative classification and centrifugal impaction is used to separatethe incoming particles into two fractions. A D₀ of about 20 microns ADwas readily achieved with this combination, which ensures that particleswhich “bounce” off the virtual impactor are elutriated by gravitationalsettling rather then re-entrained in the upwardly directed streamlinesbeing drawn over the lip at the crown of the impactor surface. A D₅₀ ofabout 10 microns AD is readily achieved over a range of windspeeds. Intesting at windspeeds of less than 10 mph, essentially all particles of10 microns or less are conveyed to the collector duct, in agreement withcalculations. All surfaces are designed and contoured aerodynamically bycomputational fluid dynamics to achieve this performance.

Turning now to the figures, FIGS. 1 through 3 are views of devicesrepresentative of the technical skill in the art and were discussedearlier as background. These figures are included for reference.

FIG. 4 depicts a first embodiment of an omnidirectional intake 40 of theinvention, shown here in elevation view. The device is seen to consistof a two-part housing with generally “bell shaped” rain bonnet plate 41having sloping walls and, nested thereunder, a baseplate 42 under thehollow, tented bonnet. Between the bonnet plate and the baseplate is aninternal manifold for classifying particles by aerodynamic size (AD).The internal manifold contains passageworks that originate from acircumferential inlet slot 43 visible at the outside edges of thehousing and which separates the bonnet and the baseplate. The inlet slotis omnidirectional so that airflow containing aerosols may enter fromany direction. Also visible is a cylindrical adaptor or mounting ring 44useful for attaching the sampling intake to a mast, or spar. Themounting ring is a hollow pipe and may be attached to a suction sourcenecessary for driving the particle collector.

Air that enters the inlet slot 43 is pulled through the internalpassageworks of the sampling manifold at a velocity determined by thecapacity of the suction source and the internal dimensions. The pathtaken by the airflow is termed the “flowpath”. In one embodiment, thevacuum source is a ½ horsepower blower which operates at a nominal drawof 750 sLpm. In other embodiments, draws of 1000 sLpm or more areconceived.

FIG. 5 depicts an omnidirectional intake of the invention in perspectiveview; showing windstreams (arrows) and eddies moving across theaerodynamically-shaped bonnet. The aerodynamics of the housing aresignificant in several respects. First, the leading circumferential edgeis isolated from the central mass of the bell housing so thatstreamlines approaching the device are readily separated between thoseentering the inlet slit and those crossing outside the housing. Somestreamlines that enter the internal passageways on the windward side ofthe device exit the device on the leeward side without capture. Asexternal windspeed increases, an angle of attack develops that isprogressively more acute, and at high windspeed, the column of airconveyed to the internal works is largely drawn from the part of theinlet slot directly facing into the wind because air entering betweenthe bonnet and the baseplate in excess of the suction capacity can exitthe opposite side. As wind direction shifts, the sampler is unaffected,always drawing air from the source direction of the wind, but at moremoderate windspeeds, the sampler becomes less selective and draws airfrom all directions.

Happily, the aerodynamic external contours 50 of the housing result fromthe form given to the internal manifold. This internal structure isdetailed in the following figures. FIG. 6 shows a cross-section of theomnidirectional intake. The dark arrows indicate the position ofstreamlines that enter the inlet slit 43. The bell-shaped bonnet 41forms a cover over the internal manifold and the baseplate 42 supports acentral column or pillar 61 that contains the central common duct 62which is coaxial with the mounting ring 44. Both the bonnet andbaseplate are mounted on a common central axis. The passageways of theintake manifold are provided with aerodynamically contoured internalstructure that will be explained below.

Surfaces of the internal manifold are contoured to direct the airstreamlines entering the inlet slit through a generally horizontalvestibule 65, into a vertical updraft section 66, and then around atopmost curve 67 that is generally greater than 180 degrees of turning.This bend is the result of the bulbous overhang 68 that forms the top ofthe vertical updraft section and connects the intake to the descendingcollector duct 62. The lower outermost lip 69 of the bulbous overhangforms a centrifugal impactor surface. By mounting the centrifugalimpactor surface in a vertical updraft, oversize particles that bounceor fall from the impactor will drop or settle to the bottom of thecentral pillar and can be swept from the base of the pillar and thevestibule by crosswinds. Rain or dew that enters the inlet slot but isexcluded from the collector duct also can serve to wash the externalpillar surfaces and vestibule free of any particle deposits, aself-cleaning feature.

FIG. 7 is a perspective CAD view of a half-section through theomnidirectional intake housing and is shown for clarity in visualizingthe internal passageworks 63 and circumferential inlet slit 43.

FIG. 8 describes the internal airways and passageworks of a preferredembodiment in more detail. The tracks of three particles entering theinlet slot are shown, as if by time lapse photography. The threeparticles differ by increasing aerodynamic size and can be characterizedas small, medium and large particles for purposes of illustration.

As shown in cross-section, all particles enter the inlet slot and areaccelerated in a convergent section 81 of the channel formed by sharpleading edges 82,83 of the bonnet 41 and baseplate 42. In thissimplified view, the largest particle (lower track 100) is seen to movefrom the inlet slot 84, through the converging section 81 formed byinside surfaces of the lips, and into a horizontal section with diffuser85, also termed a “vestibule”. Small (102) and medium particles (101)follow a similar track at first, but the tracks begin to diverge in thediffuser 85. As streamline velocity slows, the flow begins to slopeupward in a vertical turn or elbow 86 and then converge again as avertical updraft 87. The elbow is a centrifugal impactor and someparticle tracks will impact the inside wall in the elbow as shown (100).As the flow is bent to 90 degrees from horizontal and then past 90degrees when passing over a overhanging turn 88 near the top of thepassageway, speed is accelerated. At the crown 89 of the central pillarthe passageworks again narrow so that smaller particles (small dots,102′) remain entrained in the streamlines during a complete rotation ofdirection from up to down. The streamlines and any particle concentrateenters the descending collector duct (arrow, 90), drawn by suctionpressure. A flow guide 91 is used at the top center to direct theseparticles downward into the central common duct and is contoured toreduce turbulence at the point of flow separation.

In contrast, large and medium sized particles impact the external wallor aspect 92 of the central pillar. In an elastic collision, theparticle sticks to the impactor surface until dislodged or cleaned. Inan inelastic collision, the particle bounces from the surface back intothe airflow, but its velocity is reduced and it settles in response togravity, falling back along the passageway and coming to rest near thebottom of the central pillar, where it can be washed or blown out of theintake manifold, or otherwise cleaned away. The device thus serves as anelutriatively-assisted centrifugal impactor for classifying particlesand concentrating particles of interest, rejecting those particles thatare informationally poor.

The net result is that the column of air drawn through the intakemanifold is depleted of “oversize” (i.e., greater than about 20micrometers in apparent aerodynamic diameter, for example, includingbits of sand, raindrops, and more dense and inert materials) particles,which are rejected by the combined actions of elutriation andcentrifugal impaction. In contrast, particles in theinformationally-rich class (including biological cells, dispersivepowders such as chemical or biowarfare agents, and very fine vapordroplets) are received into a common central duct, where they can beassessed in flight, further concentrated, or can be conveyed to ananalytical device. Thus the sectional view shown schematicallyillustrates how the device works as a particle concentrator andclassifier. By configuring the internal manifold flowpath with criticaldimensions for a desired range of airflows, the effective particle sizeexclusion and transmission limits can be closely controlled.

As seen in the figure, the small particle track (102) exits the upflowsection of the geometry without impaction on the wall. Improvedperformance results from the presence of an anisokinetic diffusersection (85) that reduces the particle velocity at the elbow turn.Inertial effects are used to advantage to slow and direct particlesabove a cut size for the device into the outside wall of the centralpillar.

In a first preferred embodiment, designed for an airflow of 750-1250sLpm, an inlet slot of 0.75 cm was found to be highly effective inconveying particles of 10 microns (or smaller, depending on velocity andoperating conditions) through a bending passageway having a minimalcritical dimension of 0.5 cm with essentially no losses. In a secondpreferred embodiment, the device is scaled for an airflow of about 10sLpm and is designed to achieve efficient capture at Stokes numbers andhigher linear velocities of flow. Smaller or larger flows are alsoaccommodated.

The flow guide 91 is particularly useful in organizing the streamlineswithout separation eddies or effects as they enter to collector ductfrom all sides (i.e., omnidirectionally). While the view shown here is atwo-dimensional drawing, in actuality, the flowpath extends fully in theround and the vertical central pillar is essentially a frustrum of acone that has been reshaped to optimize its aerodynamic properties inexcluding particles exceeding the desired size. Organized streamlinesare more suited for forming a downstream particle beam, such as would beuseful in concentrating the informationally-rich particle fraction in anaerodynamic lens and skimmer or other particle concentrator such as areknown in the art. Of utility are the aerodynamic lenses and skimmers ofU.S. Pat. Nos. 7,875,09 and 7,704,294, which are co-assigned.

The generally broadly umbonate shape of the central pillar 61 is crownedby an annular protuberance 68, 69 that resembles a bulbous lip orcollar, which surrounds the central descending passageway forming thecollector duct 62. The male curvature of this bulbous lip is closelymated to the internal female surfaces of the housing bonnet, whichtogether form the narrow, convergingly turning passageway therebetween.Smaller particles are swept through a turn that is greater than 180degrees in the narrow turning passageway before being carried down intothe center of the device for further downstream processing.

FIG. 9 is a plot of modeling work done to show performance for particleclassification and capture efficiency, inset with a comparison to thestandard inlet of FIG. 2. For solid curves are shown, each correspondingto capture efficiency particles as a function of particle size aswindspeed is increased from 1 mph to 30 mph. Overall efficiencyapproaches 100% for 10 micron particles at windspeeds up to 20 mph anddrops to about 65% at 30 mph. Nonetheless the D₅₀ at 30 mph is stillgreater than about 11 microns. In all cases, particle exclusion isessentially complete at greater than 20 microns AD. Shown are curves forwindspeeds of 4.3 mph (95), 10.8 mph (96), 20 mph (97), and 30 mph (98).Performance of the standard inlet (FIG. 2) at 4.3 mph is shown as adotted line (99). In comparison, particle capture efficiency as afunction of size drops essentially to zero at a cut size D₀ of about 6microns, too small for capture of the most informationally-richparticles.

FIG. 10 is a plot showing measured performance versus modeledperformance for particles of 3 and 7 microns AD at a windspeed of 10mph. Computational modeling is used to predict performance and is shownby the dotted line. Experimental results for the two particle sizes areshown by solid diamonds and exceed computational predictions.

FIG. 11 describes a general rationale and methodology for use of anomnidirectional intake of the invention in an aerosol sampling protocol.

Particles existing in a moving air column are assumed to be randomlydispersed and a first function of a sampling manifold is to cleanlyisolate a subset of the streamlines destined to enter the manifoldhousing from those that will pass around, over or under the housingassembly. Not all streamlines entering the housing are captured in thecollector duct. As windspeed increases, the attack angle of the intakeis restricted to high velocity streamlines originating to the directionfrom which the wind is blowing. These are slowed in the diffuser sectionof the manifold and may then curve up and into the collector duct or beshed out the leeward side of the housing. As before, particles ridingthose streamlines, regardless of direction of origin, are classifiedaccording to size. Larger particles are selectively impacted andelutriated in the vertical updraft segment of the manifold. Thoseparticles that strike the external surfaces of the central pillar orbulbous lip are either lodged there and excluded from the airstream orbounce and settle away from the intake. Smaller particles are carried bythe streamlines around the hemi-torus of the central pillar and are notsubjected to cyclonic flow in the downslip tubing, thus minimizinglosses on the inside surfaces of the collector duct. Subsequently, thisparticle fraction, which contains the more informationally-richparticles in the aerosol population (i.e., those having an aerodynamicsize of less than 20 microns AD), can be concentrated, collected oranalyzed.

Schematically the steps for centrifugal impaction-assisted elutriativeclassification are as follows:

-   -   1. Admit a slice of a moving airstream through an        omnidirectional circumferential inlet slot and accelerate that        airstream, which is now isolated from rain and wind and is        internalized in the intake housing.    -   2. Decelerate the airstream in a diffuser and bend the        streamlines upward into a vertical passageway enclosed in the        round on one side by the bell-housing of the bonnet and on the        other side by the aerodynamically sloped outside walls of the        central pillar.    -   3. Impact oversized particle material and mist at or near the        top of the impactor surface formed by the rising outside wall of        the central pillar and bulbous annular lip or collar crowning        the central pillar and surrounding the descending collector        duct, which is located at the center axis of the housing.    -   4. Convey informationally-rich particle material with the        streamlines over the top of the bulbous lip and through a turn        of 180 degrees or more, where a flow guide is used to ensure the        streamlines separate cleanly from the roof of the bell housing        as they are directed down and into the collector duct.    -   5. Optionally, concentrate, collect or analyze the        informationally-rich particle fraction downstream from the        intake manifold.

This method is driven by a downstream suction pressure exhaust and iscontrolled by the configuration of the inlet slot and internalpassageworks within the intake housing.

Optionally, the intake housing can be connected by a pipe or channel toa collection, concentration, or analysis module. In one embodiment, thecollection module is a pair of filter membranes mounted side-by-side ina cassette that can be removed for analysis.

In other embodiments, the collector duct may comprise an annularaerodynamic lens having multiple lens elements for forming a “particlebeam”, and a skimmer for separating particle-depleted sheath flow fromthe particle rich “core flow” or particle beam, sometimes termed a“minor flow”.

FIG. 12A is a second embodiment 120 of an omnidirectional intake of theinvention. In this embodiment, the internal passageways of the intakemanifold are subdivided by radially directed wedges, the purpose ofwhich is to direct flow under windy conditions into the collector ductwithout “cross-flow” losses out the back of the intake manifold. A largefraction of the particles that enter the radial inlet section somedistance from the centerline pass between the plates and out the back ofthe inlet without entering the upflow section of the inlet. The use ofvanes 121 in the inlet slit 122 and horizontal diffuser section is foundto redirect more of these particles into the updraft section of theintake manifold, as is useful for some applications.

FIG. 12B shows a detail of one of the vanes used in the omnidirectionalintake of FIG. 12A. This vane is not configured to induce cyclonic flowbut rather to limit streamlines flowing between the bonnet and baseplatewithout interacting with the central column and impactor surfaces.Marked are the leading edge 123 and the trailing edge of the vane.

FIG. 13 describes a third embodiment 130 of the invention with internalsupport rod 131 for reversibly mounting a removable bonnet plate 132.The bonnet plate is supplied with a handle 133 and is mounted so as toslide up and out of the housing assembly. This exposes the centralpillar 134 for cleaning if required, and the axial support shaft 131 canbe fitted with cassette holders 136 for emplacing one or more filtermembranes in the collector duct airway. Periodically the filtermembranes may be removed for off-site testing. Various methods forautomated monitoring of the filter membranes are also conceived. Otherparticle traps may be emplaced in the collector duct and are accessibleafter the bonnet is removed.

FIG. 14 describes a collar assembly 141 for the central pillar 142, thecollar having a tubular ultrasonic transducer for assisted cleaning. Asshown, the collar is a ring transducer of a piezoelectric sandwichconstruction and when activated by an alternating current, expands andcontracts so as to shake the impactor zones 143 and dislodge accumulatedparticles. This can be done periodically to clean the device beforefurther use.

Also shown in FIG. 14 is a modified collector duct 144 with air-to-airparticle concentrator disposed therein. The duct is configured with acylindrical aerodynamic lens array 145 and skimmer 146 for forming aparticle beam and for shearing off the sheath flow which is exhaustedthrough the skimmer “chimney” passages 147 in the base of the housing.In this way, a dilute suspension of suspicious particles can beconcentrated ten, twenty fold or more, simplifying analysis andincreasing the sensitivity of the analysis to detect suspiciousparticles, which can be captured downstream and flagged for furtherscreening if desired.

In a typical application, the inventive omnidirectional intake 140 withinternal skimmer is intended to selectively collect informationally-richparticles on a one or more of filter membranes housed internally in areplaceable cassette downstream from the skimmer. Following collectionof a sample, the cassette is removed for analysis. Other options arewithin ordinary skill in the art and are not compiled here.

While the above is a complete description of the preferred embodimentsof the present invention, various alternatives, modifications andequivalents are possible. These embodiments, alternatives, modificationsand equivalents may be combined to provide further embodiments of thepresent invention. Therefore, in the following claims, the terms usedshould not be construed or constructed to limit the claims to thespecific embodiments disclosed in the specification, but should beconstrued and constructed to encompass and include all possibleembodiments to which such claims are entitled. Accordingly, the claimsare not limited by the specifics of the disclosure.

INCORPORATION BY REFERENCE

All of the U.S. patents, U.S. patent application publications, U.S.patent applications, foreign patents, foreign patent applications andnon-patent publications referred to in this specification and/or citedin accompanying submissions, are incorporated herein by reference, intheir entirety. When cited works are incorporated by reference, anymeaning or definition of a word in the reference that conflicts with ornarrows the meaning as used here shall be considered idiosyncratic tosaid reference and shall not supersede the meaning of the word as usedin the disclosure herein.

1. An omnidirectional wind- and rain-resistant sampling intake forcollecting an information-rich airborne particle fraction, whichcomprises a bonnet plate and a baseplate, wherein the two plates arespaced apart to form an internal manifold with flowpath therebetween andare separated by an inlet slot all around, said internal manifold havingan outlet port on a center axis, a first inside surface formed by saidbonnet plate and a second inside surface formed by said baseplate, saidinternal manifold for directing a suction airflow from said inlet slotto said outlet port along said flowpath between said inside surfaces andfor separating information-rich particles and information-poor particlestherein, wherein said internal manifold comprises: a) a horizontal flowsection for ordering said airflow into horizontal streamlines and forelutriatively removing a first cut of said information poor particlesfrom said suction airflow; b) a first centrifugal impactor sectionfluidly joining said horizontal flow section to said outlet port, saidfirst centrifugal impactor section for impactingly removing a second cutof said information poor particles from said suction airflow.
 2. Theomnidirectional sampling intake of claim 1, wherein said inlet slotcomprises upper and lower inlet lips, said upper lip formed on saidbonnet plate and said lower lip formed on said baseplate, said upper liphaving an upper lip inside surface and a said lower lip having a lowerlip inside surface, and wherein said upper inside lip surface isgenerally horizontal to a ground plane and said lower inside lip surfaceis angled up along said flow path at a generally planar angle of lessthan 45 degrees, thereby forming a converging annular entrance to saidflow path to compensate for any ground boundary layer effect and anydeflection of excluded windstreams around or over said bonnet plate. 3.The omnidirectional sampling intake of claim 1, wherein said horizontalflow section is a diffuser section, having generally diverging firstinside surface and second inside surface with increasing distance fromsaid inlet slot, said diffuser flow for slowing streamline velocity andsharpening said first cut.
 4. The omnidirectional sampling intake ofclaim 1, wherein said first centrifugal impactor section comprises anelbow section of said flowpath for bending and accelerating saidhorizontal streamlines as generally vertically-directed streamlines, andsaid elbow segment fluidly transitioning said flow path to anelutriatively-assisted impactor section, wherein saidelutriatively-assisted impactor section comprises upwardly converginginside surfaces, said first inside surface forming a generallybell-shaped female surface and said second inside surface forming agenerally pillar-shaped male surface with crown, said pillar-shaped malesurface matingly conforming to said female surface with flowpathannularly converging therebetween, wherein said crown is surrounded by aradiused annular lip projecting into said flowpath, said projectingradiused annular lip with underside impactor surface for impactinglycapturing said information-poor particles with elutriative assist,thereby excluding said informationally-poor particles from said suctionairflow and conveying said informationally-rich particles over saidradiused annular lip.
 5. The omnidirectional sampling intake of claim 4,wherein said bell-shaped female surface encloses said pillar-shaped malesurface and said crown of said pillar shaped male surface is formed witha radius and a collector duct descending centrally therethrough, saidcollector duct having fluid connection with said outlet port, andfurther wherein said bell shaped female surface is formed with a flowguide mated to said radius for acceleratingly directing streamlinesaround said crown and into said collector duct without separation eddytherein.
 6. The omnidirectional sampling intake of claim 5, wherein saidradius is extended for greater than 180 degrees of arc, therebydirecting said streamlines along a flowpath that turns for greater than180 degrees of arc.
 7. The omnidirectional sampling intake of claim 5,wherein a particle concentrator or a particle collector is disposed insaid collector duct.
 8. The omnidirectional intake of claim 1, which isself-cleaning in wind or rain.
 9. The omnidirectional intake of claim 8,wherein said inlet slot is configured with dimensions for passiveflow-through ventilation with wind-driven scouring and gravitationallydriven cleaning of said horizontal section and said first centrifugalimpactor section.
 10. The omnidirectional intake of claim 4, whereinsaid pillar-shaped male surface comprises an ultrasonic ring transduceroperatively configured for self-cleaning said underside impactorsurface.
 11. The omnidirectional intake of claim 1, wherein said bonnetplate is provided with a center mounting rod for manual placement andremoval, and optionally an external handle.
 12. The omnidirectionalintake of claim 1, wherein said intake slot comprises vertically placedvanes radially disposed therein.